Merge pull request iovisor#448 from vmg/vmg/stacks

Better stack walking APIs

examples/tracing/mallocstacks.py

@@ -0,0 +1,60 @@
+#!/usr/bin/python
+#
+# mallocstacks Trace malloc() calls in a process and print the full
+# stack trace for all callsites.
+# For Linux, uses BCC, eBPF. Embedded C.
+#
+# This script is a basic example of the new Linux 4.6+ BPF_STACK_TRACE
+# table API.
+#
+# Copyright 2016 GitHub, Inc.
+# Licensed under the Apache License, Version 2.0 (the "License")
+
+from __future__ import print_function
+from bcc import BPF, ProcessSymbols
+from time import sleep
+import sys
+
+if len(sys.argv) < 2:
+ print("USAGE: mallocstacks PID")
+ exit()
+pid = int(sys.argv[1])
+
+# load BPF program
+b = BPF(text="""
+#include <uapi/linux/ptrace.h>
+
+BPF_HASH(calls, int);
+BPF_STACK_TRACE(stack_traces, 1024)
+
+int alloc_enter(struct pt_regs *ctx, size_t size) {
+ int key = stack_traces.get_stackid(ctx,
+ BPF_F_USER_STACK|BPF_F_REUSE_STACKID);
+ if (key < 0)
+ return 0;
+
+ u64 zero = 0, *val;
+ val = calls.lookup_or_init(&key, &zero);
+ (*val) += size;
+ return 0;
+};
+""")
+
+b.attach_uprobe(name="c", sym="malloc", fn_name="alloc_enter", pid=pid)
+print("Attaching to malloc in pid %d, Ctrl+C to quit." % pid)
+
+decoder = ProcessSymbols(pid)
+
+# sleep until Ctrl-C
+try:
+ sleep(99999999)
+except KeyboardInterrupt:
+ pass
+
+calls = b.get_table("calls")
+stack_traces = b.get_table("stack_traces")
+
+for k, v in reversed(sorted(calls.items(), key=lambda c: c[1].value)):
+ print("%d bytes allocated at:" % v.value)
+ for addr in stack_traces.walk(k.value):
+ print("\t%s (%x)" % (decoder.decode_addr(addr), addr))

src/python/bcc/table.py

@@ -412,9 +412,37 @@ def __init__(self, *args, **kwargs):
  raise Exception("Unsupported")
 
 class StackTrace(TableBase):
+ MAX_DEPTH = 127
+
  def __init__(self, *args, **kwargs):
  super(StackTrace, self).__init__(*args, **kwargs)
 
+ class StackWalker(object):
+ def __init__(self, stack, resolve=None):
+ self.stack = stack
+ self.n = -1
+ self.resolve = resolve
+
+ def __iter__(self):
+ return self
+
+ def __next__(self):
+ return self.next()
+
+ def next(self):
+ self.n += 1
+ if self.n == StackTrace.MAX_DEPTH:
+ raise StopIteration()
+
+ addr = self.stack.ip[self.n]
+ if addr == 0 :
+ raise StopIteration()
+
+ return self.resolve(addr) if self.resolve else addr
+
+ def walk(self, stack_id, resolve=None):
+ return StackTrace.StackWalker(self[self.Key(stack_id)], resolve)
+
  def __len__(self):
  i = 0
  for k in self: i += 1